BOSTON (AP) — The largest health insurer in Massachusetts has cut prescriptions of narcotic painkillers by an estimated 6.6 million pills in 18 months as part of a campaign to curb abuse.

Executives from Blue Cross Blue Shield of Massachusetts say the decline in prescribed opiates including Percocet and Vicodin followed the insurer’s decision to limit the quantity of narcotic painkillers its members could obtain without approval. Patients with cancer and terminal illnesses are exempted from the limits.

Company president Andrew Dreyfus tells The Boston Globethat the insurer implemented changes in July 2012 that have reduced prescriptions by 20 percent for common opioids including Percocet, and 50 percent for longer-lasting drugs including OxyContin.Company president Andrew Dreyfus tells The Boston Globe (http://b.globe.com/1ism2Tg ) that the insurer implemented changes in July 2012 that have reduced prescriptions by 20 percent for common opioids including Percocet, and 50 percent for longer-lasting drugs including OxyContin.

Dreyfus says the program is the first of its kind in the state and possibly the country.